CRE Quality Control Procedures 2 — Questions and Answers
Question 1: Which type of control chart is most appropriate for monitoring the proportion of defective items in a variable-size sample?
- p-chart (Correct answer)
- np-chart
- c-chart
- u-chart
Correct answer: p-chart
The p-chart monitors the proportion (fraction) defective and accommodates variable sample sizes.
Question 2: In acceptance sampling, what does the Operating Characteristic (OC) curve depict?
- The probability of acceptance versus the lot defect rate (Correct answer)
- The average outgoing quality versus sample size
- The producer's risk versus consumer's risk
- The inspection cost versus lot size
Correct answer: The probability of acceptance versus the lot defect rate
The OC curve plots the probability of accepting a lot against its true defect rate, showing discrimination power.
Question 3: A process has a Cpk of 0.85. What does this indicate?
- The process is not centered and is producing defects beyond specification limits (Correct answer)
- The process is capable and centered
- The process mean equals the target value
- The process has excessive variation but no defects
Correct answer: The process is not centered and is producing defects beyond specification limits
Cpk below 1.0 indicates the process is not capable; it is producing output outside at least one specification limit.
Question 4: Which quality tool is specifically designed to determine which input variables most significantly affect an output variable?
- Design of Experiments (DOE) (Correct answer)
- Pareto chart
- Cause-and-effect diagram
- Control chart
Correct answer: Design of Experiments (DOE)
DOE systematically varies input factors to quantify their individual and combined effects on process outputs.
Question 5: What is the purpose of a gage R&R (Repeatability and Reproducibility) study?
- To quantify measurement system variation relative to process variation (Correct answer)
- To calibrate measurement equipment to NIST standards
- To determine the optimal sample size for inspection
- To validate corrective actions after a nonconformance
Correct answer: To quantify measurement system variation relative to process variation
Gage R&R assesses how much of the observed variation is due to the measurement system itself versus the actual process.
Question 6: Under MIL-STD-1916, what sampling philosophy replaced AQL-based sampling?
- Zero Acceptance Number (c=0) sampling (Correct answer)
- Continuous sampling plans
- Skip-lot sampling
- Dodge-Romig sampling
Correct answer: Zero Acceptance Number (c=0) sampling
MIL-STD-1916 promotes zero acceptance number plans, emphasizing defect prevention over detection.
Question 7: When a control chart shows a run of 8 consecutive points on one side of the centerline, this indicates:
- A non-random pattern suggesting a process shift (Correct answer)
- Normal random variation within control limits
- Excessive measurement error
- A change in sample size
Correct answer: A non-random pattern suggesting a process shift
Eight consecutive points on one side of the centerline is a Western Electric rule violation signaling a process mean shift.
CRE Quality Control Procedures 2
Which type of control chart is most appropriate for monitoring the proportion of defective items in a variable-size sample?